It is important to have an accurate reading of the fluids, such as lubricating oil, transmission shifting fluid, and coolant, associated with various pieces of equipment. It is also important to be sure that any access opening to the fluid reservoir is sealed to avoid the passage of external contaminants into the reservoir. In addition, it is important to have a closure that is easily operated and durable.
Prior art attempts at addressing all three requirement, such as those shown in U.S. Pat. Nos. 3,662,470; 6,453,740; and 6,314,808 have not met all three requirement successfully.